Various optical recording media such as DVD-RW and DVD-R can record a large volume of information and can easily retrieve data in a random access mode, and thereby have been widely used, recently, as external recording devices for information processors such as computers. For example, a typical DVD-R having an organic dye-containing recording layer has a laminated structure in which a dye recording layer and a reflective layer are disposed on a transparent substrate in this order and a protective layer covers these recording and reflective layers. Recording and reading are performed by laser light passing through the substrate. In addition, in order to increase the storage capacity of these optical recording media, multilayer optical recording media, each having a plurality of recording layers, have been developed. For example, a dual-layer optical recording medium including two dye-recording layers and an intermediate layer on a first disk transparent substrate has been reported. The intermediate layer is composed of an ultraviolet-curable resin and is disposed between the dye-recording layers.
Such a dual-layer optical recording medium can be prepared by a 2P (photo polymerization) process using a transparent stamper and by a process comprising forming two disk substrates each having a recording layer and a reflective layer stacked thereon and bonding the two disk substrates with a photo curable resign layer interposed between them.
In the both processes, the reflective layer and the dye-containing recording layer (hereinafter, referred to as a recording layer (1) or a second-layer recording layer) are stacked in this order on a substrate, which is most far from the incident face of laser light.
In the process bonding the two disk substrates each having a recording layer and a reflective layer stacked thereon, a dual-layer optical recording medium is produced by preparing a first disk substrate by stacking a recording layer and a reflective layer in this order on a substrate having guide grooves serving as recording tracks (hereinafter sometimes referred to as “conventional stack” or “conventional stack structure” by likening the transparent resin layer provided with grooves to a substrate) and a second disk substrate by laminating a reflective layer and a recording layer in this order on the other substrate (hereinafter sometimes referred to as “inverted stack” or “inverted stack structure”); applying a photo-curable resin on these disk substrates; and then attaching the resin-coated faces and curing the photo-curable resin. Optical information is written on and read from the two recording layers using a write/read light incident on the first disk substrate. This process stacking the two disk substrates does not require the transfer of an asperity pattern on a transparent stamper, unlike the 2P process, resulting in high productivity and low cost.
In the inverted stack structure, it is known that a so-called “barrier layer” is disposed between the recording layer and the photo-curable resin (see Patent Documents 1 and 2).
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-311384 (paragraphs [0052] and [0053], and Example 2)
[Patent Document 2] Japanese Patent Application Laid-Open No. 2002-373451 (paragraphs [0034] and [0035], and Example)